1. Field of Invention
The present invention relates to road haulage and, more particularly, to a system and method for determining whether the weight of a vehicle exceeds predetermined roadway weight limitations.
2. Description of Related Art
A semi-trailer is a trailer without a front axle, which is adapted to be coupled to and towed by a road tractor (also known as a “semi-truck” or simply a “truck”). A semi-trailer does not trail completely behind the road tractor. It is coupled to the road tractor at a point that is forward of the rear-most axle of the road tractor such that a portion of the weight of the trailer is carried by the rear axle(s) of the road tractor.
In North America, road tractors typically include three axles, namely: a front “steer” axle having two wheels; and a pair of rear “drive” axles, each having a pair of double wheels (“dualies”) on each side. Due to their relatively close proximity to each other, the pair of rear drive axles is generally considered as a single axle for purposes of roadway weight limit calculations. Other configurations are known.
In North America, the semi-trailer typically includes two “tandem” axles at the rear, each of which has dual wheels. However, semi-trailers having only one axle and/or only pairs of single wheels are also known. Again, due to their relatively close proximity to each other, the pair of tandem axles is generally considered as a single axle (sometimes referred to herein as the “trailer axle”) for purposes of roadway weight limit calculations. The combination of a road tractor and semi-trailer is sometimes referred to as an “eighteen wheeler” because the road tractor typically has ten wheels and the semi-trailer typically has eight wheels.
The semi-trailer is coupled to the road tractor by means of a coupling pin (also known as a “king pin”) on the front of the semi-trailer, which engages with a horseshoe-shaped coupling device called a fifth wheel, which is mounted proximal to the rear of the road tractor. The fifth wheel is slidably supported by the frame of the road tractor, and can be repositioned relative to the frame of the road tractor to adjust the weight distributed on the drive axles of the road tractor. Similarly, the tandem axle(s) on the semi-trailer are slidably supported relative to the frame of the semi-trailer and can be repositioned to adjust the weight distributed thereon and also to adjust the weight distributed to the drive axles. As noted below, the ability to accurately make such adjustments is important because the weight placed on each axle must not exceed predetermined legal roadway weight limits otherwise a fine can be imposed.
When the tandem axles on the semi-trailer are moved forward (i.e., closer to the truck) weight is shifted from the drive axles of the road tractor to the tandem axles on the semi-trailer (i.e., the tandem axle load weight becomes heavier and the road tractor drive axle weight becomes lighter). Conversely, when the tandem axles on the semi-trailer are moved backward (i.e., away from the road tractor) weight is shifted from the semi-trailer to the road tractor (i.e., the semi-trailer tandem axle load weight becomes lighter and the road tractor drive axle weight becomes heavier). When the fifth wheel is moved forward, a greater amount of weight is placed on the “steer” axle of the road tractor. When the fifth wheel is moved rearward, a lesser amount of weight is placed on the “steer” axle of the road tractor.
These adjustments are performed by the operator of the road tractor after the semi-trailer is coupled to the road tractor. Conventionally, the operator repositions the fifth wheel and tandem axles based on experience and operates the road tractor and semi-trailer until such time as the operator can obtain axle weight measurements using truck scales and make adjustments, if necessary. The lack of an ability to confirm whether the total weight of the vehicle (i.e., the combination of the road tractor and the semi-trailer) and the weight on the axles is within the legal roadway weight limits places the operator at risk of being outside the legal roadway weight limits until such time as the operator can reach the truck scales. Furthermore, the operator's time is consumed while waiting to use the truck scales, which is costly.
The prior art discloses a variety of complicated systems that are intended to assist an operator in repositioning the fifth wheel and/or the tandem axles on the semi-trailer to insure that the weight distributed to each axle does not exceed predetermined roadway weight limitations. These prior art systems, which often involve complex mechanical and/or electronic devices, have not found wide acceptance in the trucking industry ostensibly due to cost, performance and/or reliability issues. A simple system and method is needed for determining whether the axles of a road tractor and a loaded semi-trailer coupled thereto exceed predetermined roadway weight limitations.